一,非平衡面板用xtscc:
xtset idd year
panel variable: idd (unbalanced)
time variable: year, 2001 to 2007, but with gaps
delta: 1 unit
. xtscc logtfp exportstate absorb size area year klindustry ,fe
year is not regularly spaced: there are contemporaneous gap(s) across all subjects in idd
r(101).